1. Field of the Invention
This invention is concerned with a spur gear differential which is lockable to a limited extent, comprising a sun gear with external teeth, a hollow gear with internal teeth arranged coaxially to the sun gear, a planetary gear carrier arranged to be rotatable relative to both the sun gear and the hollow gear, and planetary gears carried by the carrier and meshed with the sun gear and the hollow gear.
2. Description of Prior Art
Differrentials constructed as planetary drives with the planetary gears co-operating with one of the central gears to act as a gear pump are known from DE-OS 35 42 184 and U.S. Pat. No. 3,251,244. With both these designs, the effect differs from that of conventional gear pumps because no provision has been made for a supply and discharge end, but the oil conveyed between the tooth gaps is squeezed through the gaps provided in the region of engagement between the gears. These gap losses produce a locking effect.
In other words, the locking effect is achieved as a result of the arrangement and design of the gaps. The disadvantage of the two designs mentioned above is that the locking effect occurs at any speed differential.
However, when using lockable differentials in motor vehicles, there occur operating conditions in which a continuously existing locking effect of a certain magnitude disadvantageously affects the driving behaviour of the vehicle. In particular this applies to using lockable differentials in connection with automatic anti-locking systems for the vehicle wheels.